Lean transition into PE and lean spot during WOT

[Niemer]

I have definitely seen a fuel pressure spike right before the lean condition, but only with the IDs, it doesn't seem to happen with the stock injectors.

Why would a fuel pressure spike cause the engine to go lean? And any idea what would cause it?

[DSteck]

Stock injectors have less flow variance with a pressure change. No idea what would cause it. I'm saying I bet there's a momentary dip in the pressure. Stuff like this is why I use mechanical regulators on everything.

[Niemer]

I added another fuel pressure sensor to the rail and I haven't seen any dip at the spot where it's happening. Any chance that upgrading to the 2.5bar OS could take care of this?

[Tre-Cool]

did you ever find a resolution for this? I have the exact same symptons occuring on a similar combo (albiet using a different tuning tool). I can even go as having the car running 2afr richer than required and the lean spike still occurs.

Funnily enough it also does it exactly 2.1 seconds after entering pe mode. Where the fuel has allready richened up, leans out then richens up again. Definetly not a fuel supply problem as this car has 2 internal walbro pumps.

[Niemer]

I never did, but fortunately it hasn't elevated itself to anything more than an annoyance. Sorry to hear you have the same headache I do, but it makes me feel better that I'm not alone.

[383_Stroker]

I never did, but fortunately it hasn't elevated itself to anything more than an annoyance. Sorry to hear you have the same headache I do, but it makes me feel better that I'm not alone.

Any resolution now? Ive got the same hump, also only with the id850s.

[Niemer]

Still no resolution, still get a fuel spike, but I think I may have stumbled across something related.

I did figure out the lean transition into PE, when the enrichment rate is set to '1' or thereabouts the commanded EQ ratio immediately transitions to your setpoint. The problem with that is the system can't actually make that quick of a change, so by setting the enrichment rate to something small, say 0.03, it will gradually ramp down to your desired PE EQ.

The enrichment rate isn't a time or anything like that, it is a step/step value. That is, it will subtract 0.03 from the current EQ every scan of the ECM until it reaches the desired PE EQ. Best I can figure the scan rate of the ECM is something like 50ms, so at an enrichment rate of 0.03 it would take ~1/3 of a second to transition from Stoich (EQ = 1) to EQ = 0.8, seems pretty reasonable to me.

Probably the best way to set it up is to figure out the fastest transition your setup can make into PE by setting your enrichment rate to 1 and take a log to see what the slope of the transition from Stoic to PE is, based on your wideband reading. Then play with enrichment rate to get the commanded transition to match the slope from the first log.

I did this and it seems like the hump has settled down, it's still there, but doesn't seem to peak as high.

[Maxspeed96ct]

Let me know what else you find, Ive had a similar lean stumble on my truck right at the RPM the stall flashes. And when I tried to correct it per the histogram it just goes crazy rich with any changes.

I have my Maf enable at 2700 , but ive tried 3600, 500, and its always the same

[GHuggins]

This is probably going to be a stupid question as I have not read all of the older post, but has anyone tried "stepping" up the transient tables? When I have this problem - mainly on VE only tunes and most noticeable when getting into throttle hard, say third gear then letting off to no throttle around 3500 to 4000 rpms, then immediately or soon after restomping it - you should feel a bad bucking problem from this lean spike. I go into the transients - both evap and impact with impact being the most corrective to the problem and start increasing the entire map regions starting around 80kpa by 1.1 then next by 1.25 then next by 1.45 or 1.5 then final 100kpa zone by 1.8 or 1.75. This pretty much everytime gets rid of the lean spike... The reason why I adjust the lower kpa levels is to better "blend" the transition. It's just the ecm's inability to make correct fuel corrections at the "now" quicker revving rates combined with the fact that boost is typically now involve which gets nearly all of the "stagnant" fuel particles out of the intake runners from the higher air flow.

Dial in MAF and VE with constant load and the "best" most consistant way. Use transients to make "into" boost or throttle corrections as they were intended...

[Niemer]

I gave it a shot this morning, starting at 70kPa at 1.1 and stepping up to 100kPa at 1.8, still see the spike. I noticed the gain table has an RPM axis, I wonder if bumping that up in the problem RPM ranges would have an effect.

The odd thing is that there doesn't seem to be a consistent peak some of them will go as much as 13% lean while other times it'll be around 4%

As a note, I'm running MAF only at the moment.

P.S. your shop is gorgeous.

[brentsten]

Subd for results. Exact same issue here. I thought transient fueling was only used for tip-in fueling though, not WOT?

[GHuggins]

Transient is used for everything. However if it's a specific rpm area, then your fuel map is usually or can be a little off. You can address by adding to the specific MAF and VE points or just change your PE table in the specified areas. Most will choose PE table since it's rpm specific and the quickest, dirtiest way to knock it out.

You can increase transients more than 1.8 at 100kpa and focus on both Impact and evap tables. I never need to go higher than 1.8. Depends on how far off your fuel table is (2%, 5%, higher). I have heard of some guys needing to go as high as 2.something... Read tuning how too's section - transient discussion. Prime example when boost is involved...

[383_Stroker]

I've raped my transient table, and tried stock zl1 transient tables, see no difference in lean spot. It doesn't seem to be tied to a specific maf frequency either. It's a rather odd issue lol

[GHuggins]

I've raped my transient table, and tried stock zl1 transient tables, see no difference in lean spot. It doesn't seem to be tied to a specific maf frequency either. It's a rather odd issue lol

Stock ZL1 transients are pretty close to being identical to any 6.2l.

Perhaps I need to read the post. This is happening when getting into throttle correct? Not after already in and maintaining throttle? Most likely turbocharged? If turbocharged you can use the 2bar OS upgrade and set it up for fueling with any boost.

I also adjust injection timing with turbo applications due to the same fact as the transient adjustments being required - quicker flowing air = more fuel lost out exhaust valve durring overlap. Sweet spot is somewhere right around 12 to 15 degrees retarded - makes big difference on fuel requirement under boost to maintain AF ratio. Typically won't mess with this on supercharged applications unless I'm having problems with fueling or a cam is involved. Cams combined with boost really needs this adjusted.

Is this rpm specific? If it is - go after PE table... Then I assume everyone has already raised their ramp in rates to somewhere near 1.5 or 1.7? Another pointless question I'm sure, but this does effect time into PE.

How did the gain table turn out Niemer?

[Niemer]

Perhaps I need to read the post. This is happening when getting into throttle correct? Not after already in and maintaining throttle? Most likely turbocharged? If turbocharged you can use the 2bar OS upgrade and set it up for fueling with any boost.

No, for me this happens exactly 2 seconds after PE is commanded, that is the only thing that I can find that is constant. It will happen at different MAF frequencies, RPMs, changing throttle, steady throttle, different boost levels, and the list goes on. It would be worth a read, I have done a ton of testing on this and a lot of knowledgeable people have weighed in, everyone is stumped. Unfortunately all the images that were attached to posts are gone.

I did switch to SD long ago to see if that made a difference and it did not. It would happen in various places in the fueling map, again the only thing that stayed the same was the 2 seconds after entering PE.

Haven't tested the gain table yet, I'll do that tomorrow.

This is an example of a typical spike.
spike.png

you can see the massive lean spike at the bottom, it goes from .8 to .96 lambda and back to .8 in ~0.5s, also the other thing that I didn't mention above that is always present is a fuel pressure drop then spike just before that is circled in yellow. You can also see it, but only just, in the narrowband readings.

[383_Stroker]

Stock ZL1 transients are pretty close to being identical to any 6.2l.

Perhaps I need to read the post. This is happening when getting into throttle correct? Not after already in and maintaining throttle? Most likely turbocharged? If turbocharged you can use the 2bar OS upgrade and set it up for fueling with any boost.

I also adjust injection timing with turbo applications due to the same fact as the transient adjustments being required - quicker flowing air = more fuel lost out exhaust valve durring overlap. Sweet spot is somewhere right around 12 to 15 degrees retarded - makes big difference on fuel requirement under boost to maintain AF ratio. Typically won't mess with this on supercharged applications unless I'm having problems with fueling or a cam is involved. Cams combined with boost really needs this adjusted.

Is this rpm specific? If it is - go after PE table... Then I assume everyone has already raised their ramp in rates to somewhere near 1.5 or 1.7? Another pointless question I'm sure, but this does effect time into PE.

How did the gain table turn out Niemer?

2 Seconds into PE, it leans about half a point, every single time.

[07GTS]

not sure if this will help but i noticed with mine that the 'fuel from wall stabilization' is set to 2 when i changed that to 1 it seemed like the transients reaction slowed down, then back to 2 it was faster to react so maby increasing it .5 or 1 more and see if it helps your lean spot, other than that I'm not sure what that number does

[brentsten]

I just started tuning VE with the MAF failed, but am still seeing the lean spike. I'm still on the rich side of things, but its roughly 0.8 leaner when it happens.
Screenshot when entering PE and when the spike occurs.

Pre-spike.PNG
Spike.PNG

I've yet to update my sig, but all three cars are similar. All PD blower G8s, but different cam selection, injectors, etc.

[Niemer]

Are you guys that have this issue running the stock fuel pump or something else?

[383_Stroker]

Are you guys that have this issue running the stock fuel pump or something else?

I've got a zl1 pump mechanically regulated.